1. Field of the Invention
The present invention relates to an image processing system, and in particular to an image frame synchronizing apparatus which receives images from a plurality of image sources and synchronizes image frames outputted from the plurality of image sources with an image frame outputted from one image source among the image sources, in order to display the images on a cathode ray tube (CRT) in one frame unit, and a method thereof.
2. Description of the Background Art
In general, in an image processing system which receives images from a plurality of sources at the same time, and displays one image frame among the images on a single cathode ray tube (CRT) or displays two or more image frames thereon at the same time by dividing the CRT screen, the image frames must be synchronized in order to display the image frame or image frames on the CRT whenever a user requires to view the image frame(s) of a specific image source. Here, an image frame synchronizing apparatus is used for synchronizing the image frames.
The image frame synchronizing apparatus has been recently employed in image processing systems such as a closed circuit television (CCTV) system. The conventional image frame synchronizing apparatus composing the CCTV with a screen division apparatus serves to receive images from a plurality of CCTV cameras and synchronize the image frames. The CCTV screen is divided into a certain number of regions, and different image frames are displayed on the divided regions at the same time.
The conventional image frame synchronizing apparatus will now be described in detail.
FIG. 1 illustrates an image frame synchronizing apparatus including: a plurality of A/D converters 10A, 10B, . . . , 10H receiving analog image from first to eighth sources SOURCE 1, SOURCE 2 . . . , SOURCE 8 and outputting corresponding digital signals, respectively; a synchronous signal detector 20 receiving the analog image signal from the first image source SOURCE 1 and detecting a synchronous signal therefrom; first to eighth decoders 30A, 30B, . . . 30H receiving the digital signals from the corresponding plurality of A/D converters 10A, 10B, . . . , 10H and outputting corresponding decoding signals, respectively; a video RAM module 40 with a plurality of frame memories respectively storing the decoding signals in one frame units according to the synchronous signal; and a D/A converter 50 converting digital image data into an analog image signal, the digital data being stored in the frame memory in one frame units and outputted from the video RAM module 40.
In the conventional image frame synchronizing apparatus, a reproducing signal can be inputted along with the signals from the plurality of sources. As shown in FIG. 1, the image frame synchronizing apparatus further includes a multiplexer 60 receiving an image signal from the eighth source SOURCE 8 and the reproducing signal, selecting the image or reproducing signal, and outputting the selected one to the eighth A/D converter 10H.
The above-described image frame synchronizing apparatus must be provided with as many signal paths as the sources in order to respectively receive the images from the plurality of sources and output the images as the image frames on the CRT. As a result, there is a disadvantage in that the image frame synchronizing apparatus is increased in size because the hardware corresponding to each path is used in proportion to the number of the sources outputting the image signals. There is another disadvantage of the image frame synchronizing apparatus in that it is expensive because the number of the high-priced video RAMs for respectively storing the signals processed via the paths is increased in proportion to the number of the sources or paths.
It is therefore a primary object of the present invention to provide an image frame synchronizing apparatus with two paths which receives image signals from a plurality of image signal sources and synchronizes image frames from the image signal sources with an image frame from one image signal source among the plurality of image signal sources in order to display the images on a cathode ray tube CRT in one frame unit.
It is another object of the present invention to provide an image frame synchronizing method which receives image signals from a plurality of image signal sources and synchronizes image frames from the image signal sources with an image frame from one image signal source among the plurality of image signal sources in order to display the images on a cathode ray tube CRT in one frame unit.
In order to achieve the primary object of the present invention, there is provided an image frame synchronizing apparatus including; a switch receiving and switching source image signals outputted from a plurality of image signal sources in order to output the image signals to a first output terminal and a second output terminal; a frame synchronous signal detector detecting a synchronous signal from the image signal one of the image signal source among the plurality of image signal sources; first and second A/D converters converting analog image signals to digital image signals, the analog image signals being outputted respectively from the first and second output terminals; first and second decoders decoding the digital image signals and respectively outputting first and second decoding signals; first and second buffers storing the first and second decoding signals according to the frame synchronous signal, the buffers being identical in size to an image frame; a video RAM module with two RAMs which respectively store the first and second decoding signals outputted from the first and second buffers; and a D/A converter converting an output signal from the video RAM module into an analog image signal, and outputting the converted signal to a cathode ray tube (CRT).
In order to achieve another object of the present invention, there is also provided an image frame synchronizing method including the steps of: a switching step of separately outputting image signals from a plurality of image signal sources to a first path and a second path; a synchronous signal detecting step of receiving an image signal from one of the image signal source among the plurality of image sources and detecting a frame synchronous signal therefrom; a first processing step of generating and storing a first decoding signal by respectively decoding a frame image of the image signals inputted to the first path, and outputting the first decoding signal according to the synchronous signal; a second processing step of generating and storing a second decoding signal by respectively decoding a frame image of the image signals inputted to the second path, and outputting the second decoding signal according to the frame synchronous signal; a third processing step of alternately storing the first and second decoding signals outputted in the first or second processing steps, and alternately outputting the thusly stored signals; and a converting step of converting the signals outputted in the third processing step into signals which can be displayed on a cathode ray tube (CRT).